One class of magnetic memory devices receiving increased attention in the recent period is the so-called magnetic tunnel junction (MTJ) devices. These devices may include multiple magnetic layers, such as metal layers, as well as insulating layers. During fabrication, an interlevel dielectric (ILD) layer may be used to provide electrical isolation (insulation) between MTJ devices or between MTJ device and other conductive layers. In addition, a protection layer may be used as a barrier between the ILD material and an MTJ device. The protection layer may encapsulate an MTJ device and may prevent degradation of the magnetic properties of an MTJ device caused by diffusion of moisture from the ILD material. During high temperature processing subsequent to forming an MTJ device stack, the protection layer may also prevent the out-diffusion of metal materials used in the MTJ device.
Silicon nitride (SiN) films have been widely used as a protection layer, in part because the silicon nitride may act as a diffusion barrier in preventing oxidation of an MTJ device stack. A plasma enhanced chemical vapor deposition process (or, simply, plasma enhanced chemical vapor deposition), sometimes referred to as PECVD is the most commonly used technique for forming an encapsulating SiN film, where a combination of silane (SiH4) and ammonia (NH3) may be employed. This may result in adequate film quality and conformality over the MTJ device being coated. One side effect of the SiN film deposition process is the degradation of magnetic anisotropy of an MTJ device, such as when a CoFeB alloy layer is used in the MTJ device. In particular metal interfaces may be damaged during encapsulation due to a number of factors, including reactive radical reaction, high reactivity of radicals due to elevated temperatures employed in the PECVD process, as well as high energy ions or other species impinging on the MTJ device. With respect to these and other considerations the present improvements may be useful.